Patterned, synthetic longitudinally exchange biased GMR sensor

ABSTRACT

Patterned, longitudinally and transversely antiferromagnetically exchange biased GMR sensors are provided which have narrow effective trackwidths and reduced side reading. The exchange biasing significantly reduces signals produced by the portion of the ferromagnetic free layer that is underneath the conducting leads while still providing a strong pinning field to maintain sensor stability. In the case of the transversely biased sensor, the magnetization of the free and biasing layers in the same direction as the pinned layer simplifies the fabrication process and permits the formation of thinner leads by eliminating the necessity for current shunting.

This is a division of patent application Ser. No. 10/104,802, filingdate Mar. 22, 2002 now U.S. Pat. No. 6,857,180, Transverse OrLongitudinal Patterned Synthetic Exchange Biasing For Stabilizing GmrSensors, assigned to the same assignee as the present invention, whichis herein incorporated by reference in its entirety.

RELATED PATENT APPLICATION

This application is related application with Ser. No. 10/091,959, filingdate Mar. 06, 2002, now issued as U.S. Pat. No. 7,035,060; toapplication with Ser. No. 10/077064, filing date Feb. 15, 2002, nowissued as U.S. Pat. No, 7,010,848; and to application with Ser. No.10/116,984, filing date Apr. 05, 2002, now issued as U.S. Pat. No.6,842,969; assigned to the same assignee as the current invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the fabrication of a giantmagnetoresistive (GMR) magnetic field sensor for a magnetic read head,more specifically to the use of either transverse or longitudinalsynthetic exchange biasing to stabilize, suppress side reading andreduce the magnetic track width (MRW) of such a sensor.

2. Description of the Related Art

Magnetic read heads whose sensors make use of the giant magnetoresistiveeffect (GMR) in the spin-valve configuration (SVMR) base their operationon the fact that magnetic fields produced by data stored in the mediumbeing read cause the direction of the magnetization of one layer in thesensor (the free magnetic layer) to move relative to a fixedmagnetization direction of another layer of the sensor (the fixed orpinned magnetic layer). Because the resistance of the sensor element isproportional to the cosine of the (varying) angle between these twomagnetizations, a constant current (the sensing current) passing throughthe sensor produces a varying voltage across the sensor which isinterpreted by associated electronic circuitry. The accuracy, linearityand stability required of a GMR sensor places stringent requirements onthe magnetization of its fixed and free magnetic layers. The fixedlayer, for example, has its magnetization “pinned” in a direction normalto the air bearing surface of the sensor (the transverse direction) byan adjacent magnetic layer (typically an antiferromagnetic layer) calledthe pinning layer. The free layer is typically magnetized in a directionalong the width of the sensor and parallel-to the air bearing surface(the longitudinal direction). Layers of hard magnetic material(permanent magnetic layers) or laminates of antiferromagnetic and softmagnetic materials are typically formed on each side of the sensor andoriented so that their magnetic field extends in the same direction asthat of the free layer. These layers, called longitudinal bias layers,maintain the free layer as a single magnetic domain and also assist inlinearizing the sensor response by keeping the free layer magnetizationdirection normal to that of the fixed layer when quiescent. Maintainingthe free layer in a single domain state significantly reduces noise(Barkhausen noise) in the signal produced by thermodynamic variations indomain configurations. A magnetically stable spin-valve sensor usingeither hard magnetic biasing layers or ferromagnetic biasing layers isdisclosed by Zhu et al. (U.S. Pat. No. 6,324,037 B1) and by Huai et al.(U.S. Pat. No. 6,222,707 B1).

The importance of longitudinal bias has led to various inventionsdesigned to improve the material composition, structure, positioning andmethod of forming the magnetic layers that produce it. One form of theprior art provides for sensor structures in which the longitudinal biaslayers are layers of hard magnetic material (permanent magnets) thatabut the etched back ends of the active region of the sensor to producewhat is called an abutted junction configuration. This arrangement fixesthe domain structure of the free magnetic layer by magnetostaticcoupling through direct edge-to-edge contact at the etched junctionbetween the biasing layer and the exposed end of the layer being biased(the free layer). Another form of the present art employs patterneddirect exchange bias. Unlike the magnetostatic coupling resulting fromdirect contact with a hard magnetic material that is used in the abuttedjunction, in exchange coupling the biasing layer is a layer offerromagnetic material which overlays the layer being biased, but isseparated from it by a thin coupling layer of conducting, butnon-magnetic material. This non-magnetic gap separating the two layersproduces exchange coupling between them, a situation in which it isenergetically favorable for the biasing layer and the biased layerassume a certain relative direction of magnetization. Another form ofexchange coupling involves a direct contact between the freeferromagnetic layer and an overlaying layer of antiferromagneticmaterial. Xiao et al. (U.S. Pat. No. 6,322,640 B1) disclose a method forforming a double, antiferromagnetically biased GMR sensor, using as thebiasing material a magnetic material having two crystalline phases, oneof which couples antiferromagnetically and the other of which does not.Fuke et al. (U.S. Pat. No. 6,313,973 B1) provides an exchange coupledconfiguration comprising a coupling film, an antiferromagnetic film anda ferromagnetic film and wherein the coupling film has a particularlyadvantageous crystal structure.

As the area density-of magnetization in-magnetic recording media (eg.disks); continues to increase, significant reduction in the width of theactive sensing region (trackwidth) of read-sensors becomes necessary.For trackwidths less than 0.2 microns (μm), the traditional abuttedjunction hard bias structure discussed above becomes unsuitable becausethe strong magnetostatic coupling at the junction surface actually pinsthe magnetization of the (very narrow) biased layer (the free layer),making it less responsive to the signal being read and, thereby,significantly reducing the sensor sensitivity.

Under very narrow trackwidth conditions, the exchange bias methodbecomes increasingly attractive, since the free layer is not reduced insize by the formation of an abutted junction, but extends continuouslyacross the entire width of the sensor element. FIG. 1 is a schematicdepiction of an abutted junction arrangement and FIG. 2 is an equallyschematic depiction of a direct exchange coupled configuration. As canbe seen, the trackwidth in the abutted junction is made narrow byphysically etching away both ends of the sensor, whereas in the exchangecoupled sensor, the trackwidth is defined by placement of the conductiveleads and bias layers while the sensor element retains its full width.

The direct exchange biasing-also has disadvantages when used in a verynarrow trackwidth configuration because of the weakness of the pinningfield, which is found to be, typically, approximately 250 Oe. Thepresent invention will address this weak pinning field problem whileretaining the advantages of exchange biasing by providing a new exchangebiased configuration, synthetic exchange biasing. In this configuration,the biasing layer is exchange coupled to the free layer byantiferromagnetic exchange coupling, in which the ferromagnetic biasinglayer and the ferromagnetic free layer are coupled by a non-magneticlayer to form a configuration in which the two layers have antiparallelmagnetizations (a synthetic antiferromagnetic layer). A stronger pinningfield, typically exceeding 700 Oe, can be obtained using the syntheticexchange biasing method. More advantageously, an effective magnetictrackwidth of 0.15 μm can be obtained with a physical track width of 0.1μm by using such a configuration by reducing the level of side reading(sensor response generated by signals originating outside of themagnetic trackwidth region) which is produced by the portion of the freelayer that is beneath the biasing layer and conduction leads. Theinvention provides such a novel synthetic exchange biased sensor in twoconfigurations, longitudinal and transverse, each of which is shown tohave particular advantages both in its operation and its formation.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a magneticallystable patterned synthetic exchange biased GMR sensor capable of readinghigh area density magnetic recordings of densities exceeding 60 Gb/in²(gigabits per square inch).

It is a second object of the present invention to provide such apatterned synthetic exchange biased GMR sensor which is biased in eitherthe longitudinal or the transverse directions.

It is a third object of the present invention to provide such asynthetic exchange biased GMR sensor having a very narrow effectivemagnetic trackwidth in which undesirable side reading is significantlyreduced.

It is a fourth object of the present invention to provide such asynthetic exchange biased GMR sensor that is easily fabricated.

It is a fifth object of the present invention to provide such asynthetic exchange biased GMR sensor that has thin conducting leadlayers for an improved topography.

The objects of this invention will be achieved in three embodiments,each of which will now be briefly described and will then be describedin fuller detail below. In the first embodiment, a synthetic exchangelongitudinally biased GMR sensor will be provided, said sensor having abottom spin valve, specularly reflecting structure which can bedeposited in a single fabrication process and which has the followingstructural form:

-   -   NiCr/MnPt/CoFe(AP2)/Ru/CoFe(AP1)/Cu/CoFe—NiFe/Ru/CoFe/IrMn/Ta/Au        The NiCr is a seed layer, the MnPt is an antiferromagnetic        pinning layer for the bottom synthetic pinned layer of CoFe        (AP2)/Ru/CoFe(AP1), wherein the two ferromagnetic exchange        coupled CoFe layers are labeled AP1 & AP2 to distinguish them.        The Cu layer is a conducting, non-magnetic spacer layer        separating the synthetic pinned layer from the CoFe—NiFe        ferromagnetic free layer (a bilayer). This latter bilayer is        antiferromagnetically exchange coupled across a Ru layer to a        (pattered) CoFe biasing layer, forming the synthetic exchange        coupled bias structure which has both a high pinning field and        advantageous magnetostriction characteristics. The exchange        biased layer is itself antiferromagnetically pinned by direct        exchange coupling with an antiferromagnetic IrMn layer, over        which is a conductive lead layer of Ta/Au. It is found that the        pinning field of the free layer provided by the patterned bias        layer in this synthetic exchange coupled configuration exceeds        650 Oe and may be as high as 755 Oe, as compared to pinning        fields of the order of 250-300 Oe for the direct (not synthetic)        coupled structure.

In the second embodiment, a synthetic exchange transversely biased GMRsensor will be provided together with a method for its fabrication. Thestructural form of this embodiment is:

-   -   NiCr/AFM/CoFe(AP2)/Ru/CoFe(AP1)/Cu/CoFe—NiFe/Ru/CoFe/AFM/Ta/Au.        The NiCr is a seed layer, AFM denotes an antiferromagnetic        pinning layer for the bottom synthetic pinned layer of CoFe        (AP2)/Ru/CoFe(AP1), wherein the two ferromagnetic exchange        coupled CoFe layers are labeled AP1 & AP2 to distinguish them.        The Cu layer is a conducting, non-magnetic spacer layer        separating the synthetic pinned layer from the CoFe—NiFe        ferromagnetic free layer (a bilayer). This latter bilayer is        antiferromagnetically exchange coupled across a Ru layer to a        (patterned) CoFe biasing layer, forming the synthetic exchange        coupled bias structure. The exchange biased layer is itself        antiferromagnetically pinned by direct exchange coupling with an        antiferromagnetic layer, again denoted AFM, over which is a        conductive lead layer of Ta/Au. In contrast to the structural        form of the first embodiment, the same antiferromagnetic        material, typically either IrMn or MnPt, can serve in both        locations designated AFM. An important advantage of the        transverse biasing is that the magnetic field of the free and        pinned layers are in the same direction, producing a plateau        region under low external field wherein the free layer        magnetization and the pinned layer magnetizations do not rotate        relative to each other. This is particularly important for        reducing signal contributions from the free layer region that is        under the biasing layer which then produces a narrow effective        trackwidth.

It is another one of the advantages of this second embodiment thatdifferent antiferromagnetic materials are not necessary to achieve itsobjects because both the synthetic pinned layer, CoFe(AP2)/Ru/CoFe(AP1), and the synthetic bias exchange coupled free layer,CoFe—NiFe/Ru/CoFe, are magnetized along the same direction. This allowsantiferromagnetic materials with high blocking temperatures to beutilized which, in turn, allows high pinning fields to be obtained. Thehigh pinning fields minimizes the problems caused by sensor current flowwithin the sensor element and, consequently, current shunting is notrequired and thin conducting lead layers can be used. The thirdembodiment of the present invention provides a transversely biasedsensor as in the second embodiment, but the pinning fields at oppositeends of the free layer are antiparallel to each other. Thisconfiguration affords the additional advantages of stabilizing the biaspoint of the free layer and further minimizing side reading by thesensor. In the description of the three embodiments provided below, thestructures, the processes preferred for their fabrication and theiradvantages, will be more fully described.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment, as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanying figures,wherein:

FIG. 1 is a highly schematic diagram of a prior-art abutted junction GMRsensor stack having a hard magnetic longitudinal bias layer andconductive lead overlayer in contact with the junction. The diagram is across-sectional view of the air bearing surface (ABS) of the sensor. Thesensor stack shows only the free layer.

FIG. 2 is a schematic, ABS view, cross-sectional diagram of a prior-artdirect exchange (longitudinally) biased GMR sensor stack, showing thepatterned biasing layers, their magnetization directions, and otherlayers of the sensor.

FIG. 3 a is a schematic, ABS view, cross-sectional diagram of asynthetic exchange (longitudinally) biased GMR sensor stack, beforepatterning, fabricated in accord with the objects of the first preferredembodiment of the present invention.

FIG. 3 b shows the process of patterning the sensor of FIG. 3 a.

FIG. 4 a is a schematic, ABS view, cross-sectional diagram of asynthetic exchange biased GMR sensor stack formed in accord with asecond embodiment of the present invention. The transversemagnetizations of the exchange biased free layer and the syntheticpinned layer are indicated.

FIG. 4 b is the sensor stack of FIG. 4 a subsequent to patterning.

FIG. 5 a is a schematic, ABS view, cross-sectional diagram of apartially formed synthetic exchange biased GMR sensor stack formed inaccord with a third embodiment of the present invention. In thisembodiment the transverse magnetizations of each lateral end of theexchange biased free layer are antiparallel to each other and each isalso antiparallel to the transverse magnetizations of the biasing layersthat overlay them.

FIGS. 5 b-5 e show the detailed processes by which the sensor stack of 5a is patterned and magnetized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1 there is shown a schematic cross-sectionalview of the ABS surface of a typical abutted junction GMR sensordesigned in accord with the prior art. As can be seen, the narrowtrackwidth is obtained at the price of reducing the physical width ofthe ferromagnetic free layer (10). As a result, the biasing layer (25)pins the magnetization of the free layer and reduces the sensitivity ofthe sensor.

Referring next to FIG. 2, there is shown a schematic cross-sectionalview of the ABS surface of a patterned direct exchange longitudinallybiased GMR sensor of the prior art. The physical trackwidth (10) of thisconfiguration is defined by the width of the region between the leads(20), typically a Ta/Au bilayer, and the patterned biasing layersbeneath them (25), typically layers of CoFe. The ferromagnetic freelayer (27), typically a CoFe/NiFe bilayer, extends the entire width ofthe sensor so it is not adversely affected by the edge pinning field ofthe biasing layer, which is a disadvantage of the hard biased abuttedjunction of FIG. 1. The diagram also shows the antiferromagnetic layer(29), typically a layer of IrMn, which pins the patterned biasing layer(25). The free layer (27) is separated from the biasing layer (25) by anon-magnetic coupling layer (28) which is typically a layer of Cu or Ruand which directly exchange couples the ferromagnetic free layer (27) tothe ferromagnetic biasing layer (25) by ferromagnetic coupling toproduce parallel magnetizations (11) labeled M2 (biasing layer) and M1(free layer). The remainder of the configuration comprises anantiferromagnetically coupled (synthetic) pinned layer (30), whichcomprises two ferromagnetic layers ((32) and (34)) antiferromagneticallyexchange coupled across a non-magnetic coupling layer (36) and which isseparated from (27) by a non magnetic spacer layer (31). Beneath (30)there is an antiferromagnetic pinning layer (40), typically a layer ofMnPt, which pins the antiferromagnetically coupled pinned layer. Themagnetic moments of the antiferromagnetically coupled pinned layers arein the transverse direction (perpendicular to the plane of the figure)and are antiparallel, with the directions of magnetization of theindividual layers indicated by circles (15) (out of the plane) andcrosses within circles (17) (into the plane). Obtaining perpendicularityof the free layer magnetization and pinned layer magnetizationcomplicates the fabrication process of the sensor, since two differentantiferromagnetic materials with different blocking temperatures aretypically required for (40) and (29), eg. IrMn and MnPt in thisillustration, as are different annealing schedules so that themagnetization of the pinned layer should not affect the magnetization ofthe biasing layer. When the physical trackwidth (10) of this entireconfiguration is narrow, however, (less than 0.2 microns) the strengthof the ferromagnetic coupling (the pinning field) is weak and istypically less than 250 Oe. Note that thicknesses are not given for thisfigure since the configuration is shown for comparison purposes only.

First Preferred Embodiment

Referring next to FIG. 3 a, there is shown a schematic cross-sectionalview of the air bearing surface (ABS) of a synthetic exchangelongitudinally biased GMR sensor, before patterning, fabricated inaccord with the objects of a first embodiment of the present inventionand having the properties and advantages of said embodiment. The deviceis fabricated in a sequence of three major steps: 1) depositing thesensor layers; 2) annealing and magnetizing the synthetic pinned layerand the synthetic biased free layer; 3) patterning.

1) Deposition Process

First there is deposited a seed layer (9), which is typically a layer ofNiCr deposited to a thickness of between approximately 55 and 65angstroms with 60 angstroms being preferred. On this seed layer is thendeposited a first antiferromagnetic layer (40) to serve as a pinninglayer. Typically this pinning layer is a layer of MnPt deposited to athickness of between approximately 80 and 150 angstroms with 100angstroms being preferred. On the pinning layer, and pinned by it, thereis then formed a synthetic antiferromagnetic pinned layer (30), which isan antiferromagnetically coupled trilayer comprising a firstferromagnetic layer (32), a first non-magnetic antiferromgneticallycoupling layer (36) formed on (32) and a second ferromagnetic layer (34)formed on the coupling layer. The ferromagnetic layers are typicallylayers of CoFe, with the first layer having a thickness of betweenapproximately 12 and 20 angstroms with 15 angstroms being preferred andthe second layer having a thickness of between approximately 15 and 25angstroms with 20 angstroms being preferred. The coupling layer, whichis typically a layer of Ru, is formed to a thickness of betweenapproximately 7 and 9 angstroms with 7.5 angstroms being preferred. Onthe synthetic pinned layer is then formed a non-magnetic spacer layer(31), which separates the pinned and free layers. This spacer layer istypically a layer of Cu, which is formed to a thickness of betweenapproximately 13 and 25 angstroms with 18 angstroms being preferred. Thefree layer (27), which is a ferromagnetic bilayer of CoFe (22) and NiFe(23), is then formed on the spacer layer, wherein the CoFe layer has athickness of between approximately 5 and 15 with 10 angstroms beingpreferred and the NiFe layer has a thickness of between approximately 15and 30 angstroms with 20 angstroms being preferred. The free layer isthen antiferromagnetically exchange coupled across a non-magneticcoupling layer (28) to a ferromagnetic biasing layer (25), forming,thereby, the synthetic exchange biased configuration (26). The couplinglayer in this case is a layer of Ru of thickness between approximately 7and 9 angstroms with 7.5 angstroms being preferred and the biasing layeris a layer of CoFe of thickness between approximately 10 and 25angstroms with 15 angstroms being preferred. The synthetic exchangebiased configuration (26) is then pinned by an antiferromagnetic layerof IrMn (29) of thickness between approximately 35 and 55 angstroms with40 angstroms being preferred. A conducting lead layer (20) is depositedover the IrMn layer in a lead overlay (LOL) configuration. The leadlayer is typically a Ta/Au bilayer of thickness between approximately100 and 500 angstroms.

2) Annealing Process

The GMR sensor configuration thus formed is then given a first pinnedlayer annealing to fix the magnetizations of both synthetic pinnedlayers (30) & (26). The anneal consists of a 5 hour 280° C. anneal in anexternal transversely directed magnetic field of approximately 10 kOe(kilo-oersteds) to set both pinned layers in the transverse direction(perpendicular to the air-bearing surface). The resulting magnetizationvectors are shown only for the first pinned layer (30) as a circle (15),representing a direction out of the plane, and a circle with an interiorcross (17), representing a direction into the plane. Following thisfirst pinned layer anneal, a second anneal is applied at a lowertemperature and lower magnetic field to reset the magnetization of thesynthetic exchange biased layer (26) from the transverse direction intothe longitudinal direction. This second anneal is carried out for a timeof approximately 30 minutes at an annealing temperature of approximately250° C., which is higher than the IrMn blocking temperature. Theresulting magnetizations are shown as arrows, M1 (12) being themagnetization of the free layer and M2 (11) that of the biasing layer.Under this anneal, the synthetic pinned layer (30) retains itstransverse magnetization. It is found by experiment that theconfiguration described above, under the sequence of anneals to which itis subjected as is also described above, has the advantageous propertiesof a high pinning field that is approximately 755 Oe, as well as adesirable value of free-layer magnetostriction.

3) Patterning Process

Referring now to FIG. 3 b, there is shown a schematic diagramillustrating the process by which a physical trackwidth (10) ofapproximately 0.1 microns is formed in the sensor of FIG. 3 a by etchingthe lead and pinning layers to form the patterned exchange structure.Patterning is done by sequentially removing the entire thickness of alateral portion of the lead layer (40) (shown in dashed outline) and theentire thickness of the IrMn pinning layer beneath it (42) (shown indashed outline) by use of a reactive ion etch (RIE) or an ion beam etch(IBE). Removal of these two layers exposes a portion of the CoFe biasinglayer (44), said portion then being effectively removed by an oxidationprocess, which converts it to a non-magnetic CoFeO (shown shaded). Inthis process, the antiferromagnetically coupling layer (28) of Ru actsas an oxidation barrier to prevent the oxidation from extending downwardto adversely affect the ferromagnetic free layer (27). The surface ofthe coupling layer (28) beneath (44) is thereby itself oxidized at thetermination of the process. Note in the synthetic pinned layer (30) thatsmall circles (15) represent magnetizations out of the plane, circleswith interior crosses (17) are into the plane. The symbols M1 (12) andM2 (11) refer to the antiparallel directions of the magnetizations ofthe free (M1) and pinning (M2) layers.

Second Preferred Embodiment

Referring next to FIG. 4 a, there is shown a schematic cross-sectionalview of the air bearing surface (ABS) of a synthetic exchangetransversely biased GMR sensor, before patterning, fabricated in accordwith the objects of a second embodiment of the present invention andhaving the properties and advantages of said embodiment. The device isfabricated in a sequence of three major steps: 1) depositing the sensorlayers; 2) annealing and magnetizing the synthetic pinned layer and thesynthetic biased free layer; 3) patterning.

1) Deposition Process

First there is deposited a seed layer (9), which is typically a layer ofNiCr deposited to a thickness of between approximately 50 and 60angstroms. On this seed layer is then deposited a firstantiferromagnetic layer (40) to serve as a pinning layer. Typically thispinning layer is a layer of MnPt deposited to a thickness of betweenapproximately 100 and 150 angstroms, but other antiferromagneticmaterials such as NiMn, PdPtMn, FeMn or IrMn can be used. On the firstpinning layer, and to be pinned by it, there is then formed a syntheticantiferromagnetic pinned layer (30), which is an antiferromagneticallycoupled trilayer comprising a first ferromagnetic layer (32), a firstnon-magnetic antiferromagnetically coupling layer (36) formed on (32)and a second ferromagnetic layer (34) formed on the coupling layer. Theferromagnetic layers are typically layers of CoFe, with the firstferromagnetic layer having a thickness of between approximately 15 and20 angstroms with 15 angstroms being preferred and the secondferromagnetic layer having a thickness of between approximately 20 and25 angstroms with 20 angstroms being preferred. The first couplinglayer, which can be a layer of Ru, is formed to a thickness of betweenapproximately 7 and 9 angstroms with 7.5 angstroms being preferred.Alternatively, the first coupling layer can be a layer of Rh, formed toa thickness of between 4 and 6 angstroms with 5 angstroms beingpreferred. On the synthetic antiferromagnetic pinned layer there is thenformed a non-magnetic spacer layer (31), which separates the pinned andfree layers. This spacer layer is typically a layer of Cu, which isformed to a thickness of between approximately 15 and 22 angstroms with18 angstroms being preferred. The free layer (27), which is preferably aferromagnetic bilayer of CoFe (22) and NiFe (23), is then formed on thespacer layer, wherein the CoFe layer has a thickness of betweenapproximately 5 and 15 with 10 angstroms being preferred and the NiFelayer has a thickness of between approximately 15 and 30 angstroms with20 angstroms being preferred. The free layer is thenantiferromagnetically exchange coupled across a second non-magneticcoupling layer (28) to a ferromagnetic biasing layer (25), forming,thereby, the synthetic exchange biased configuration (26). If the firstnon-magnetic coupling layer (36) is a layer of Ru, then the secondnon-magnetic coupling layer (28) is also a layer of Ru of thicknessbetween approximately 7 and 8 angstroms with 7.5 angstroms beingpreferred. If the first coupling layer is a layer of Rh, then the secondcoupling layer is also a layer of Rh of a thickness between 4 and 6angstroms with 5 angstroms being preferred. If the second coupling layeris Ru, the biasing layer (25) is a layer of CoFe of thickness betweenapproximately 15 and 30 angstroms with 15 angstroms being preferred. Ifthe second coupling layer is Rh, the biasing layer (25) is a layer ofCoFe of thickness between approximately 25 and 30 angstroms with 28angstroms being preferred. It is to be noted that the thicker biasinglayer (25) formed in conjunction with the Rh coupling layer produces agreater pinning field in the sensor.

The synthetic exchange biased configuration (26) is then pinned by asecond pinning layer, which is an antiferromagnetic layer of MnPt (25)of thickness between approximately 80 and 100 angstroms with 100angstroms being preferred (note, if any of the other antiferromagneticmaterials mentioned above have been used to form the first pinninglayer, that same material can also be used here to form the secondpinning layer). A conducting lead layer (20) is deposited over the MnPtlayer (25) in a lead overlay (LOL) configuration. The lead layer istypically a Ta/Au/Ta trilayer of thickness between approximately 200 and400 angstroms.

2) Annealing Process

The GMR sensor configuration thus formed is then given a pinned layerannealing to fix the magnetization of both synthetic pinned layers (26)& (30), which are, respectively, the antiferromagnetic pinned layer andthe synthetic exchange biased configuration. The anneal consists of a 5hour 280° C. anneal in an external magnetic field of approximately 10kOe (kilo-oersteds) to set both pinned layers in the transversedirection (perpendicular to the air-bearing surface). The resultingmagnetization vectors are shown as circles (53&57) representingmagnetizations out of the plane, and circles with interior crosses(51&55) representing magnetizations into the plane. M1 and M2 are thelabels representing the magnetizations of the free and biasing layersrespectively. It is found by experiment that the configuration describedabove, under the anneal to which it is subjected as is also describedabove, has the advantageous properties of a high pinning field that ismore than 1000 Oe, as well as an effective trackwidth of less than 0.15microns subsequent to the patterning that will now be described. Asignificant advantage of the transverse directions of both the free andpinned layers is that there is a plateau of very little relativerotation of their magnetizations under small external magnetic fields.This plateau is particularly important in the region of the free layerdirectly beneath the biasing layer in that it leads to extremely smallsignals being produced by this portion of the free layer. Since unwantedside reading is a direct result of signals emanating from the extremelateral portions of the free layer, this diminution of signals from thatportion is directly responsible for the narrow effective trackwidth.Another important advantage of the transverse directions of both thefree and pinned layers is that it is unnecessary to rotate the freelayer magnetization with a second anneal after fixing the magnetizationof the pinned layer. This allows the use of antiferromagnetic pinninglayers of the same high blocking temperature material to be used to pinboth the synthetic pinned layer and the synthetic exchange biased freelayer. In turn, this allows high external fields to be used to fix thepinning field, which increases the efficacy of the biasing layer andreduces the effective trackwidth of the sensor. It has also beendemonstrated that the high pinning fields thus obtained (exceeding 1000Oe) eliminate the need for current shunting of the sensor current, whichpermits the use of thinner conducting lead layers and provides a moreadvantageous topology.

3) Patterning Process

Referring now to FIG. 4 b, there is shown a schematic diagramillustrating the process by which a physical trackwidth (10) ofapproximately 0.1 microns is formed in the sensor of FIG. 4 a bypatterning the lead and pinning layers to form the patterned exchangestructure. Patterning is done by sequentially removing the entirethickness of a lateral portion of the lead layer ((40) shown in dashedoutline) and the entire thickness of the MnPt pinning layer beneath it((42) shown in dashed outline) by use of a reactive ion etch (RIE) or anion beam etch (IBE). Removal of these two layers exposes the CoFebiasing layer (42), the portion of which is exposed ((44) shown shaded)being then effectively removed by an oxidation process, which convertsit to non-magnetic CoFeO. In this process, the antiferromagneticallycoupling layer (28) of Ru (or Rh) acts as an oxidation barrier toprevent the oxidation from extending downward to the ferromagnetic freelayer (27) and adversely affecting it. The exposed surface of thecoupling layer (28) is thereby itself oxidized at the termination of theprocess.

Third Preferred Embodiment

Referring next to FIG. 5 a, there is shown a schematic cross-sectionalview of the air bearing surface (ABS) of a partially fabricatedsynthetic exchange transversely biased GMR sensor, before theantiparallel magnetization of its biasing layer and before deposition ofa conducting lead layer and final patterning, fabricated in accord withthe objects of a third embodiment of the present invention and havingthe properties and advantages of said embodiment. In this embodiment thetransverse magnetizations of the pinning layer and free layer areantiparallel to each other at the opposite ends of the sensor where theyare beneath the conducting lead layers. This configuration has beenshown to have two advantages: 1) prevention of the bias point shift atthe center active region of the free layer and 2) minimization of sidereading at both sides of the sensor element.

The device is fabricated in a sequence of four steps: 1) depositing thesensor layers up to and including the exchange biasing layer (shown inFIG. 5 a); 2) separately magnetizing both lateral ends of the exchangebiasing layer in opposite transverse directions using a two-steppatterning and annealing sequence (shown in FIGS. 5 b and 5 c); 3)depositing conducting lead layers (shown in FIG. 5 d); 4) patterning(FIG. 5 d).

1) Deposition Process

Referring to FIG. 5 a and looking vertically upward, there is first seendeposited a seed layer (9), which is typically a layer of NiCr depositedto a thickness of between approximately 50 and 60 angstroms. On thisseed layer is then deposited a first antiferromagnetic layer (40) toserve as a pinning layer. Typically this pinning layer is a layer ofMnPt deposited to a thickness of between approximately 100 and 150angstroms, but other antiferromagnetic materials such as NiMn, PdPtMn,FeMn or IrMn can be used. On the first pinning layer there is thenformed a synthetic antiferromagnetic pinned layer (30), which is anantiferromagnetically coupled trilayer comprising a first ferromagneticlayer (32), a first non-magnetic antiferromagnetically coupling layer(36) formed on (32) and a second ferromagnetic layer (34) formed on thecoupling layer. The ferromagnetic layers are typically layers of CoFe,with the first ferromagnetic layer having a thickness of betweenapproximately 15 and 20 angstroms with 15 angstroms being preferred andthe second ferromagnetic layer having a thickness of betweenapproximately 20 and 25 angstroms with 20 angstroms being preferred. Thefirst non-magnetic antiferromagnetically coupling layer, which can be alayer of Ru, is formed to a thickness of between approximately 7 and 9angstroms with 7.5 angstroms being preferred. Alternatively, the firstcoupling layer can be a layer of Rh, formed to a thickness of between 4and 6 angstroms with 5 angstroms being preferred. In either case, thelayer is formed of a material and to a thickness that will cause the twoferromagnetic layers to align their magnetizations in an antiparalleldirection upon annealing. On the synthetic pinned layer there is thenformed a non-magnetic spacer layer (31), which separates the pinned andfree layers. This spacer layer is typically a layer of Cu, which isformed to a thickness of between approximately 15 and 22 angstroms with18 angstroms being preferred. The free layer (27), which in thispreferred embodiment is a ferromagnetic bilayer of CoFe (22) and NiFe(23), is then formed on the spacer layer, wherein the CoFe layer has athickness of between approximately 5 and 15 with 10 angstroms beingpreferred and the NiFe layer has a thickness of between approximately 15and 30 angstroms with 20 angstroms being preferred. The free layer isthen antiferromagnetically exchange coupled across a second non-magneticcoupling layer (28) to a ferromagnetic biasing layer (25), forming,thereby, the synthetic antiferromagnetic exchange biased configuration(26). If the first non-magnetic coupling layer (36) is a layer of Ru,then the second non-magnetic coupling layer (28) is also a layer of Ruof thickness between approximately 7 and 8 angstroms with 7.5 angstromsbeing preferred. If the first coupling layer is a layer of Rh, then thesecond coupling layer is also a layer of Rh of a thickness between 4 and6 angstroms with 5 angstroms being preferred. If the second couplinglayer is Ru, the biasing layer (25) is a layer of CoFe of thicknessbetween approximately 15 and 30 angstroms with 15 angstroms beingpreferred. If the second coupling layer is Rh, the biasing layer (25) isa layer of CoFe of thickness between approximately 25 and 30 angstromswith 28 angstroms being-preferred. It is to be noted that the thickerbiasing layer (25) formed in conjunction with the Rh coupling layerproduces a greater pinning field in the sensor. At this point in thefabrication process the magnetization of the pinned layer can be set byan anneal in the same manner as in the previous embodiments. A 5 houranneal in a 10 kOe magnetic field at a temperature of 280° C. ispreferred.

Referring now to FIG. 5 b, there is shown an upper portion of thestructure of FIG. 5 a wherein a lateral portion (60) of theferromagnetic biasing layer (25) has been covered by a layer of etchresistant material (62) (such as photoresist), leaving the remainingportion (shown shaded) of the biasing layer uncovered (64). Thisuncovered portion is then cleaned by a sputter etch process.

Referring next to FIG. 5 c, there is shown the cleaned portion (64)refilled with the same ferromagnetic material of the biasing layer andcovered by an additional layer of antiferromagnetic material (66), suchas a layer of IrMn deposited to a thickness Of between approximately 35and 55 angstroms with 40 angstroms being preferred, to act as a pinninglayer. During this deposition process, the fabrication thus produced isannealed in a first transverse magnetic field in a first transversedirection to fix the direction of the magnetizations in theantiferromagnetic coupling between the portion of the biasing layer(64), whose magnetization is shown as a circle (68), and thecorresponding portion of the free layer (27) beneath it, whoseantiparallel magnetization is shown as a circle with a cross (69). Thefirst anneal is for between approximately 30 and 60 minutes but whereapproximately 30 minutes is preferred, at a temperature of betweenapproximately 250° C. and 280° C., but where 250° C. is preferred andwith a magnetic field of between approximately 250 and 500 Oe but where250 Oe is preferred. The antiferromagnetic layer (66) pins the biasinglayer in this process.

Referring next to FIG. 5 d, there is shown the fabrication of FIG. 5 c,wherein the surface of the opposite lateral portion (72) of the biasinglayer is now exposed, while the remainder of the layer, which hasalready been magnetized, is covered by a resistant layer (74), such as alayer of photoresist. In a similar fashion to that described in FIG. 5c, the portion (72) is cleaned and covered with additional biasingmaterial and, over it, a layer of antiferromagnetic pinning material(75) such as IrMn is formed in a manner identical to that described inFIG. 5 c. During the deposition process a second external magnetic fieldin the opposite direction to that used in the process of FIG. 5 c isapplied and the biasing layer portion (72) is thereby magnetized in thedirection of that magnetic field (circle with a cross (81)) and the freelayer beneath it (27) is oppositely magnetized (circle (83)). The secondanneal, like the first, is for between approximately 30 and 60 minutesbut where approximately 30 minutes is preferred, at a temperature ofbetween approximately 250° C. and 280° C., but where 250° C. ispreferred and with a magnetic field of between approximately 250 and 500Oe but where 250 Oe is preferred. The deposited antiferromagnetic layer(75) serves to pin the biasing layer by this process.

Referring now to FIG. 5 e, there is shown the fabrication of FIG. 5 dwherein a central portion (85) of the twice magnetized biasing layer isremoved by an ion beam or chemical etching process to form a trackwidthof desired dimension. A conducting lead layer (90) has been formed overthe two biasing layers. The lead layer is typically a Ta/Au/Ta trilayerof thickness between approximately 200 and 400 angstroms.

As is understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in fabricating a synthetic, patterned,longitudinally or transversely exchange biased GMR sensor with narroweffective trackwidth, while still providing a method for fabricatingsuch a synthetic, patterned, longitudinally or transversely exchangebiased GMR sensor with narrow effective trackwidth, in accord with thespirit and scope of the present invention as defined by the appendedclaims.

1. A patterned, synthetic longitudinally exchange biased GMR sensor withnarrow effective trackwidth comprising: a substrate; a seed layer ofNiCr formed to a thickness between approximately 50 and 65 angstroms; afirst layer of antiferromagnetic material formed on the seed layer, saidlayer being a first antiferromagnetic pinning layer and said layer beinga layer of MnPt formed to a thickness between approximately 80 and 150angstroms; a synthetic antiferromagnetic pinned layer formed on saidfirst antiferromagnetic pinning layer, the magnetization of said pinnedlayer being pinned in a transverse direction by exchange coupling tosaid first antiferromagnetic pinning layer; a non-magnetic spacer layerformed on said pinned layer; a ferromagnetic free layer formed on saidnon-magnetic spacer layer; a non-magnetic antiferromagnetically couplinglayer formed on said ferromagnetic free layer; a longitudinal biasinglayer formed on said coupling layer, said biasing layer being formed astwo discrete, disconnected and laterally separated ferromagneticsegments, laterally and symmetrically disposed to either side of theantiferromagnetically coupling layer and wherein said segments areseparated by a portion of said biasing layer which has been renderednon-magnetic and defines a physical trackwidth and wherein theferromagnetic segments of said biasing layer are longitudinallymagnetized and antiferromagnetically exchange coupled to said free layerthrough said antiferromagnetically coupling layer to form a syntheticantiferromagnetic exchange biased configuration; a patternedantiferromagnetic pinning layer of IrMn formed to a thickness betweenapproximately 35 and 55 angstroms as two separate, disconnectedsegments, wherein a segment is formed on each ferromagnetic segment ofsaid patterned, longitudinal biasing layer and is extensively coexistingwith said segment, and wherein each of said patterned antiferromagneticlayer segments is exchange coupled to said longitudinal biasing layersegment thereby maintaining said longitudinal magnetization directions;a conductive lead layer formed on said antiferromagnetic layer andcoextensive with it.
 2. The sensor of claim 1 wherein the syntheticantiferromagnetic pinned layer is a trilayer comprising a first layer ofCoFe, formed to a thickness of between approximately 12 and 20 angstromsand a second layer of CoFe formed to a thickness of betweenapproximately 15 and 25 angstroms, with a layer of Ru between saidlayers of thickness between approximately 7 and 9 angstroms.
 3. Thesensor of claim 1 wherein the non-magnetic spacer layer is a layer of Cuformed to a thickness of between approximately 13 and 25 angstroms. 4.The sensor of claim 1 wherein the ferromagnetic free layer is a bilayercomprising a layer of CoFe of thickness between approximately 5 and 15angstroms, on which is formed a layer of NiFe of thickness betweenapproximately 15 and 30 angstroms.
 5. The sensor of claim 1 wherein thenon-magnetic antiferromagnetically coupling layer is a layer of Ruformed to a thickness of between 7 and 9 angstroms.
 6. The sensor ofclaim 5 wherein the patterned ferromagnetic longitudinal biasing layeris a layer of CoFe formed to a thickness between approximately 10 and 25angstroms.